#include <stddef.h>
#include <stdio.h>

void f(FILE *file){
    enum { BUFFER_SIZE = 1024 };
    wchar_t wbuf[BUFFER_SIZE];
    const size_t size = sizeof(*wbuf);
    const size_t nitems = sizeof(wbuf);
    size_t nread = fread(wbuf,size,nitems,file);
    /* ... */
}